1. Field of the Invention
This invention relates to the recycling and reuse of water with ammonium compounds and traces of uranium as is produced by the hydrolysis of UF.sub.6 and subsequent treatment with ammonia to precipitate ADU. There is substantially no loss of uranium by reason of such reuse, the problems of the disposal of the waste water with its toxic fluoride and radioactive materials, are avoided.
2. Description of the Prior Art
In preparing fuel elements for nuclear reactors it is desirable to employ UO.sub.2 for this purpose. A widely used method is to process UF.sub.6 to prepare ADU which is then calcined and reduced to UO.sub.2. In preparing ADU, enriched UF.sub.6 gas is reacted with water to produce an aqueous uranyl fluoride (UO.sub.2 F.sub.2) solution which is then treated with an excess of ammonium hydroxide to cause a precipitate of ADU which is recovered as an aqueous slurry. The precipitate can be filtered out or centrifuged from the aqueous phase of the slurry. The resulting waste water contains a high concentration of fluorides, primarily as NH.sub.4 F, with excess ammonia, and small quantities of dissolved uranium.
The disposal of this waste water entails considerable problems and difficulty because of the toxicity of the fluorides as well as the excess ammonia and the small but significant quantities of radioactive uranium. On both ecological and health accounts it would be highly desirable to eliminate or greatly reduce this disposal problem, as well as to recover from the waste water substantially entirely the traces of enriched uranium, which latter is a very costly material as well as being a health hazard.
U.S. Pat. No. 3,726,650 to Welty and U.S. Pat. No. 3,758,664, disclose processes for producing ADU from UF.sub.6, and their teaching is incorporated herein. They show that for each 100 pounds of UF.sub.6 converted to ADU, there is produced from between 680 to 3311 pounds of waste water solution containing approximately some 63 pounds of NH.sub.4 F and 24.8 pounds of NH.sub.4 OH.
The Hollander U.S. Pat. No. 3,394,997 also discloses processes for converting UF.sub.6 to ADU and for reclaiming some of the waste water. In this patent, an ion exchange column is employed first to recover any ADU. Then lime is applied to the waste water, in an amount of not less than required to stoichiometrically precipitate all of the fluorides. Calcium dissolved in the water remains in the system and if reused would be carried over into the ADU process where it is not desired. Even so, some 525 pounds of waste water from thickener 40 in U.S. Pat. No. 3,394,997 must go to radioactive waste burial. The shortcomings and difficulties, however, in this patent process are that substantial amounts of calcium are present in the thickener overflow going to the ammonia recycle. It is important that practically no calcium be present in the water to be reacted with UF.sub.6. Also in this patent process there are a large number of process steps for treating the waste water which are costly, requiring both extra equipment with added maintenance and service problems.